The influence of the place-value structure of the Arabic number ...

ehavioural performance in the NBT: First, classification was systematically faster and less
error prone for triplets staying within the same decade (e.g. 23_26_29 vs._25_28_31), and
second for triplets with a relatively smaller problem size (e.g. 11_14_17 vs. 81_84_87). In
summary, the results of Nuerk and co-workers (2002) suggest that apart from a crucial
involvement of magnitude manipulations, also numerical information from other sources (e.g.
multiplicativity, procedural rules) is monitored and recruited where beneficial.
For the present study, these six numerical determinants of behavioural performance in
the NBT have been selected to investigate their neuronal correlates. Three neural networks
incorporating different aspects of these numerical determinants can be distinguished: first, a
fronto-parietal network including the intraparietal cortex bilaterally, involved in magnitude
processing. Second, the superior frontal and inferior parietal cortex, including the left angular
gyrus, which subserves monitoring and applying of procedural rules as well as inhibiting
cognitive sets, and finally, the right ventrolateral prefrontal cortex subserving cognitive set
changes. Following this differentiation, predictions on the impact of the six determinants
introduced above on the activation within each of the three neural networks can be derived:
Range: A large bisection range should lead to a stronger fMRI signal in the intraparietal
cortex as more difficult magnitude manipulations are required. Additionally, activation is
expected to extend to the posterior superior parietal lobule due to more large-scale navigation
on the mental number line (Dehaene et al., 2003). Probably, activation in prefrontal regions as
well as in the SMA and pre-SMA regions may be observed, which can be associated with task
difficulty (Garavan, Ross, & Stein, 1999). In contrast, when bisection range is small, the
intraparietal cortex should be less engaged. Moreover, activation in the inferior parietal
lobule, particularly in the left angular gyrus should increase as smaller, less complex
problems were to be solved (Qin et al., 2004).
Problem size: Since the frequency of occurrence of a number decreases as its
magnitude increases (Dehaene and Mehler, 1992), the representation of relatively smaller
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